Measurements of N(⁴S) absolute density in a 2.45 GHz surface wave discharge by optical emission spectroscopy

Abstract

We have generated a N 2 flowing discharge sustained by surface waves employing a 2.45 GHz high frequency source. The N 2 dissociation was studied in the discharge and post-discharge regions by optical emission spectroscopy (OES) as a function of the experimental parameters: discharge power (30-160 W) and absolute pressure (1-20 Torr), at 0.5 Slm −1 flow rate. The N(2p 3 4 S 0 ) absolute density was measured in the discharge by actinometry. We have introduced the effect of the N 2 (X 1 + g ) vibrational temperature in the actinometry equation. Such a consideration was made based on the work of Catherinot and Sy (1979 Phys. Rev. A 20 1511) which presents a profound discussion about the quenching mechanism of the N(3p 4 S 0 ) by N 2 (X 1 + g , v) states. The 811.5 nm Ar and 821.6 nm N lines, from 2p 9 → 1s 5 and 3p 4 P 0 → 3s 4 P transitions have been utilized here. Both are easily observed in the surface wave discharge. Further, the NO chemical titration was carried out in the late post-discharge furnishing the N(2p 3 4 S 0 ) absolute density in that region. The extinction point of the 580.4 nm band of the N 2 1st positive system was measured. The density values obtained by actinometry are validated by comparison with those measured in the post-discharge region. The two sets of data, function of pressure and discharge power, may be related by the mass conservation equation. The work provides the experimental N(2p 3 4 S 0 ) absolute density values as a function of power and pressure only by application of OES techniques. Moreover, we demonstrate here that the N(3p 4 P 0 ) state is quenched by N 2 (X 1 + g , v 2) molecules forming N 2 (b 1 u , v = 0) and N( 4 S) states, in agreement with Catherinot and Sy.

Characterization of an N2flowing microwave post-discharge by OES spectroscopy and determination of absolute ground-state nitrogen atom densities by TALIF

“…This can be explained by an excess energy transferred from the electrons to the neutrals leading to an increase in discharge length as the power increases. A similar behaviour has been observed by Levaton et al [29] in flowing nitrogen microwave discharge and by Rousseau et al [30] in a microwave discharge operated in argon.…”

Nitrogen dissociation degree in the diffusion region of a helicon plasma source obtained by atomic lines to molecular band intensities ratio

“…Note that in Eq. Similar conclusions were reported by Levanton et al 40 for the 3s 4 P and 2p 4 P levels 41 reported efficient quenching of the 3p 4 S 0 state by N 2 ͑X , ജ 2͒ ͑k N q = 6.5ϫ 10 −9 cm 3 s −1 ͒. Assuming a Maxwellian eedf, Czerwiec et al 12 calculated the rate coefficients for the first three processes and found that excitation from metastable states and dissociative excitation is one to two orders of magnitude smaller than excitation rates from the ground state for electron temperatures larger than 2 eV.…”

Neutral and Excited Molecules and Atoms Densities in the Positive Column of Flowing N2 DC Discharges

“…The degree of dissociation at the end of the positive column is 0.4% at p = 230 Pa (first experimental condition) and 0.02% at p = 530 Pa (second experimental condition). The decrease in the degree of dissociation of the discharge with increasing pressure was also observed in the flowing nitrogen microwave discharge [20]. We compared the calculated degree of dissociation of the first experimental condition (0.4%) with that one found by Kumar et al [6] experimentally.…”